In 3GPP (3rd Generation Partnership Project) being a standardization project of a mobile communication system, the introduction of the inter-terminal (Device to Device: D2D) proximity service has been studied as a new feature in release 12 or later (see Non Patent Literature 1).
The D2D proximity service (D2D ProSe) is a service that enables direct inter-terminal communication in the synchronous cluster including a plurality of synchronized user terminals. The D2D proximity service includes the D2D discovery procedure (Discovery) configured to discover the proximity terminal and the D2D communication (Communication) being the direct inter-terminal communication.
By the way, the user terminal has a problem that the transmission and the reception of the D2D radio signal cannot be performed at the same time in the D2D proximity service (what is called, the Half-Duplex problem). For this reason, in the In-coverage scenario where all user terminal forming a synchronization cluster including a plurality of synchronized user terminals are located in the cell coverage, it is discussed that the base station assigns the time and frequency resources for transmitting the D2D radio signal. The base station assigns the time and frequency resources so that a plurality of user terminals configured to transmit the D2D radio signal at the same timing in the synchronization cluster do not exist, whereby the Half-Duplex problem can be solved.